Vol. 31: 259–270, 2016 ENDANGERED SPECIES RESEARCH Published November 28 doi: 10.3354/esr00768 Endang Species Res OPENPEN ACCESSCCESS A shift in foraging behaviour of beluga whales Delphinapterus leucas from the threatened Cumberland Sound population may reflect a changing Arctic food web Cortney A. Watt1,2,*, Jack Orr2, Steven H. Ferguson1,2 1Department of Biological Sciences, University of Manitoba, Winnipeg, MB R3T 2N2, Canada 2Fisheries and Oceans Canada, 501 University Crescent, Winnipeg, MB R3T 2N6, Canada ABSTRACT: Cumberland Sound, an inlet on Baffin Island, Nunavut, Canada, is undergoing changes in sea ice cover, which is affecting the marine food web. A small population of beluga whales Delphina pterus leucas inhabits Cumberland Sound year round and this population is cur- rently listed as threatened. Relatively little is known about the foraging behaviour of these belugas, but we expected that food web changes, primarily an increased abundance of capelin in the region, would have an impact on their diet and dive behaviour. We evaluated fatty acids in blubber sam- ples collected from subsistence-hunted belugas in Cumberland Sound from the 1980s to 2010, and analyzed satellite tag information from 7 belugas tagged in 2006 to 2008 to gain a better under- standing of their foraging behaviour. There was a change in the fatty acid profile of beluga blubber from the 1980s compared to the 1990s and 2000s. Specific fatty acids indicative of capelin and Arc- tic cod increased and decreased over time respectively, suggesting an increased consumption of capelin with a reduction in Arctic cod in summer in more recent years. Dive behaviour suggested different foraging tactics across seasons. Shallow short dives occurred in summer, which may indi- cate foraging on capelin, while deeper longer dives were made in autumn and winter, possibly indicating foraging on deeper prey such as Arctic cod and Greenland halibut. Potentially, autumn and winter are important foraging seasons for belugas, amassing energy reserves as blubber and creating a possible competitive conflict for resource use between belugas and expanding commer- cial fisheries. KEY WORDS: Diet · Fatty acids · Diving · Fisheries competition · Capelin · Arctic cod · Greenland halibut INTRODUCTION of the sound, and in winter belugas move towards the mouth of Cumberland Sound (Richard & Stewart Cumberland Sound is an inlet on the east coast of 2008). Whales in this population have been listed as Baffin Island, Nunavut, Canada. This region is a bio- threatened by the Committee on the Status of Endan- logically productive area and is an important summer gered Wildlife in Canada (COSEWIC 2004) as a feeding area for many animals (Cobb 2011). Beluga result of low population numbers (759 to 1960 indi- whales Delphinapterus leucas are ubiquitous in the viduals) (DFO 2005, Richard 2013, Marcoux et al. Arctic, and there is a small population that inhabits 2016). It is estimated there were >5000 belugas in Cumberland Sound year round (Richard & Stewart this population prior to large commercial hunting 2008). Whales spend summer in the northwestern catches between 1920 and 1960, while subsistence part of Cumberland Sound, particularly in Clearwa- hunts with managed quotas have been in place since ter Fiord. In autumn, whales are located in the centre the early 1980s with hunts of <50 individuals per year © C. A. Watt, S. H. Ferguson and Fisheries and Oceans Canada *Corresponding author: [email protected] 2016. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 260 Endang Species Res 31: 259–270, 2016 (Mitchell & Reeves 1981, DFO 2002). There are also decline may be a result of an increased reliance on concerns regarding boat noise and competition with capelin as a primary prey resource. This also corre- Greenland halibut Reinhardtius hippoglossoides fish- lates with evidence suggesting that capelin had low eries, a potential prey of beluga whales (Heide- abundance in Cumberland Sound in the early 2000s, Jørgensen & Teilmann 1994). but had substantially increased in abundance by Climate change is also having impacts on the food 2011 (Ulrich 2013). web in Cumberland Sound. A reduction in sea ice in Along with chemical techniques such as stable iso- the Arctic has resulted in a northward shift of subarc- tope and fatty acid analysis, diet can also be assessed tic species that can compete with and displace Arctic by evaluating dive behaviour. Determining the species (Perovich & Richter-Menge 2009, Tivy et al. depths to which whales are diving can provide an 2011, McKinney et al. 2012). For example, in north- idea of where in the water column they are foraging ern Hudson Bay the incidence of capelin Mallotus and subsequently determine what common prey are villosus increased from the mid-1980s to the late available at those depths (Watt et al. 2015). No eval- 1990s, with a subsequent decrease in Arctic cod uation of dive behaviour with respect to bottom Boreo gadus saida (Gaston et al. 2003). Similarly, in bathymetry has been conducted on belugas from Cumberland Sound the food web has been changing Cumberland Sound; however, dive data from belu- and there has been an increase in capelin and a gas in other regions has been analyzed with respect reduction in Arctic cod (McKinney et al. 2012, Ulrich to bottom bathymetry. In the Canadian High Arctic, 2013). Specifically, capelin were absent in the stom- beluga whales have been tagged and researchers achs of Arctic char Salvelinus alpinus from the Cum- found characteristic deep dives to the bottom that berland Sound region in the early 2000s, but made they interpreted as foraging dives (Martin & Smith up the bulk of their diet in 2011, and char are known 1992, 1999, Martin et al. 1998). In Hudson Bay, 2 pop- to forage opportunistically, resulting in a diet that ulations of whales were found to have different dive reflects prey availability in their environment behaviour. One of the populations used the entire (Rikardsen et al. 2007, Ulrich 2013). These changes water column when close to shore but spent more will undoubtedly affect the diet and behaviour of the time close to the sea floor when offshore, while beluga whales inhabiting the region. another population seemed to use the entire water Beluga whales are considered to have a more column regardless of distance from shore (Bailleul et diverse diet than other Arctic cetaceans (Laidre et al. al. 2012). Other belugas tagged in Hudson Bay made 2008). Arctic cod B. saida tends to dominate diet for consistent dives to the bottom (Kingsley et al. 2001), belugas from the eastern Beaufort Sea (Loseto et al. suggesting foraging on prey in the benthos. In the 2009, Quakenbush et al. 2015) and the Canadian eastern Chukchi Sea, Citta et al. (2013) found no dif- High Arctic (Matley et al. 2015). Pacific herring Clu- ference in the depths to which beluga whales of dif- pea pallasii, tomcod Microgadus tomcod (Huntington ferent sexes or ages dove, and diving depths sug- & The Communities of Buckland, Elim, Koyuk, Point gested whales foraged primarily from 200 to 1000 m. Lay and Shaktoolik 1999), rainbow smelt Osmerus However, Hauser et al. (2015) did find differences in mordax, Arctic cod B. saida, and saffron cod Eleginus the diving behaviour of adult belugas versus imma- gracilis are common dietary items for different bel- ture whales from the eastern Chukchi Sea, with uga stocks from Alaska (Quakenbush et al. 2015), adults spending significantly more time at deeper while halibut R. hippoglossoides, shrimp Pandalus depths. Hauser et al. (2015) were also able to corre- borealis, and redfish Sebastes marinus were found in late beluga dives to the distribution of Arctic cod and beluga stomachs from Greenland whales (Heide-Jør- found that whales significantly targeted depths (200 gensen & Teilmann 1994). Relatively little is known to 300 m) with maximum cod abundance. about diet from beluga whales in Cumberland Dive behaviour was investigated from 1998 to 1999 Sound, but fatty acid analysis on a small number of in a few beluga whales (n = 13) from Cumberland samples (n = 15) from 1983 to 1987 suggests that Arc- Sound (Heide-Jørgensen et al. 2001). Although the tic cod was prevalent in diet (Kelley et al. 2010). Sta- authors did not evaluate diving in relation to bottom ble isotope analysis on skin and muscle tissues from bathymetry, they did determine that belugas from Cumberland Sound belugas from 2000 to 2010 sug- Cumberland Sound spend less time at the surface at gests that diet consists primarily of Arctic cod and night compared to day, with a trend towards more capelin M. villosus (Marcoux et al. 2012). Marcoux et night dives, suggesting this may be an important al. (2012) also found a significant decline in δ15N val- time for foraging (Heide-Jørgensen et al. 2001). In ues from 1982 to 2009 and they suggested this addition, when compared to whales from other Watt et al.: Cumberland Sound beluga diet and diving 261 regions in the Canadian High Arctic, Cumberland abdominal region was collected, frozen, and sent to Sound whales had higher dive rates and these rates the Freshwater Institute, Winnipeg, MB, where sam- did not seem to change seasonally, although only 4 ples were stored at −20°C. Blubber was subsampled tags recorded dive information in the winter and only from these larger cores; a cube of blubber from the for a short time (final transmission on 1 January 2000) deepest (closest to the muscle) and most interior por- (Heide-Jørgensen et al. 2001). There was annual tion of the core (which excluded all exterior blubber variability in dive rates for Cumberland Sound that may have been oxidized over time) was used for whales but this was based on a very small sample analysis.